Prioritization of taonga myrtle species in response to myrtle rust in New Zealand

  • Pōhutukawa flowers

Myrtle rust is a highly invasive plant pathogen (Austropuccinia psidii) that infects species of Myrtaceae family. Originally from Central and South America (Glen et al. 2007) it has spread around the world, infecting our close neighbours Australia and New Caledonia in 2016 and was first identified here in May 2017. Since then, the disease has been found at 123 locations, the majority in Taranaki with a second significant area of infection in the Bay of Plenty. There have also been a small number of detections in Northland and Waikato.

The risk this pathogen poses to New Zealand myrtaceae (mānuka, rātā, pōhutukawa, ramarama, lilly pilly), as well as, commercially-grown species such as eucalyptus cannot be overstated. The pathogen can kill infected plants, has long-term impacts on the regeneration of young plants and seedlings and is very difficult to control.

New Zealand myrtaceae were used extensively by Māori as medicine, food and for construction. The species have significant cultural value for Māori and are taonga (treasured entities). Taonga include tangible things such as land, waters, plants, wildlife and cultural works, and intangible things such as language, identity and culture, including Mātauranga Māori (traditional Māori knowledge).

In the Māori worldview, man is said to descend from Tāne, the god of the forest. Therefore people and all other things in the environment have a shared common ancestry. These whanau (family) based linkages mean the virtues of respect and responsibility for nature, are inherent. Respect for mauri, tapu, kaitiakitanga, whanaungatanga, manaakitanga, and aiopipi are expressions of these virtues (Patterson 1994). Because of these linkages, diseased trees affect Māori the same way as having a family member affected by a disease. It can have negative consequences on our hauora (health/ wellbeing) and quality of life.

Indigenous worldviews and concerns around the impacts of myrtle rust are underrepresented in literature. Apart from a short paragraph on the threat to Hawai’ian indigenous culture (Loope 2010), there is no other literature on the impact of P. psidii to Australian Aboriginal or other Pacific Island communities and cultures.

Clark (2011) identified the economic and environmental impacts of the myrtle rust incursion and the consequences of the incursion for New Zealand. However, the sociocultural consequences for Māori have not been fully explored.

Through an extensive engagement process Hone Ropata and Alby Marsh have gained an insight into what Māori want in a response plan to the myrtle rust incursion and a prioritization strategy for native New Zealand myrtaceae.

The prioritization strategy they are proposing has three main themes.

Prioritization of places

Click to enlarge
Figure 1: Map of New Zealand showing climate suitability for Austropuccina psidii under current (1971-1990) climate averages as indicated by the CLIMEX Ecoclimatic Index, published by Kriticos & Leriche (2008). Green overlays indicate current hotspots for Austropuccina psidii as of September 2017, Kerikeri in Northland; Te Puke in the Bay of Plenty; Te Kuiti in Waikato; and New Plymouth in Taranaki.

The majority of our effort should be focused in areas where myrtle rust is present, with areas, supported by literature, of favourable climatic conditions a priority.

Prioritization of species/genera

Since being discovered on mainland New Zealand, the Ministry for Primary Industries and the Department of Conservation have tracked known occurrences of infection by host species and geographic location. Prioritising plant species most susceptible to the myrtle rust infection was the general consensus. These plants, in susceptibility order, (based on confirmed numbers) are:

  • Lophomyrtus bullata
  • Metrosideros spp.
  • Callistemon spp.
  • Syzygium smithii
  • Agonis flexuosa
  • Eucalyptus sp.
  • Leptospermum scoparium

Prioritization of special individuals and populations

“It was impressed upon us that there are individual species and native populations of myrtaceae in regional New Zealand that are of significant cultural importance. A considerable effort needs to be applied to ensure their conservation” says Hone.

Examples of these taonga are:

  • Te rerenga wairua Te Rerenga Wairua at Cape Reinga ( very tip of the North Island) is the most spiritually significant place in New Zealand and is marked by an ancient pohutukawa tree (Metrosideros excelsa). It is believed that after death, all Māori spirits travel to the Cape where the spirit (wairua) makes its final flight (rerenga) before moving on to the next stage of its journey.
  • Te Waha-o-Rerekohu Te Waha-o-Rerekohu, situated at Te Araroa on the east coast is said to be the oldest living pohutukawa tree (at least 600 years old). Planted there while a marae still stood at the site, the tree presently resides on the grounds of a school.
  • Bartlett’s Rata — this species is endemic to New Zealand with only three known forest remnants, near Cape Reinga. In 2012 there were only 25 adult Bartlett’s rata left in the wild. This was a decrease from the 34 mature individuals known in 1992. This species has been declared critically endangered by the ICUN and is threatened for many reasons:
    • The species is at severe risk from browsing animals and fire.
    • In the past, land clearance has also threatened this species.
    • The species is vulnerable due to minimal genetic variation in the population.
    • Bartlett’s rata requires cross pollination, and this combined with a decrease in the number of nectar-feeding birds to pollinate the flowers has led to low seed production.

The official response to the incursion will also have potential consequences for Māori communities. As Albie points out “Restrictions on moving plants between rohe is potentially of great concern to iwi, especially those that rely on the health of plant nurseries to sustain their peoples financially as well as iwi that have placed time and resource into environmental conservation efforts”.

"By no means is this prioritization strategy complete. There are many questions that need to be answered before we can begin to move on to asking the next logical set of questions".

“Knowing if and how myrtle rust affects the wood of infected trees will be important. We need to know if the traditional uses of these taonga will still be viable or even if we can still use the wood” says Albie.

This work is important to both the indigenous as well as scientific communities interested in learning from one another through the sharing of knowledge, both traditional and modern.

References

Clark S 2011. Risk analysis of the Puccinia psidii/ Guava Rust fungal complex (including Uredo rangelii/Myrtle Rust) on nursery stock. Ministry of Agriculture and Forestry, Wellington, New Zealand.
Kriticos DJ, Leriche A. (2008). The current and future potential distribution of guava rust, Puccinia psidii in New Zealand. Rotorua, New Zealand: Scion. MAF Biosecurity New Zealand Technical Paper, (2009/28).
Loope L. (2010). A summary of information on the rust Puccinia psidii Winter (guava rust) with emphasis on means to prevent introduction of additional strains to Hawaii (No. 2010-1082, pp. 1-31). US Geological Survey.
Patterson J. (1994). Maori environmental virtues. Environmental Ethics, 16(4), 397-409.